The present invention is directed to a system and method for detecting airborne allergen particles and for providing an alarm or operating a filtering system if the detected amount of allergen particles is above a predetermined level.
Many individuals suffer from allergies to airborne particles such as dust, pollen and the like which are often present in the environmental air breathed by the individual. The majority of particulates to which many individuals are sensitive are typically in the 5 to 50 micron range. The presence of such particles in air breathed by sensitive or allergic individuals may give rise to a plethora off symptoms such as asthma, coughing, sneezing, as well as skin rashes and anaphylaxis. Knowledge or warning of the presence of high levels of allergenic particles in the environmental air is helpful to such individuals, potentially enabling them to take medication, leave the area, or activate allergen removing filters before the onset of serious symptoms.
In U.S. Pat. No. 5,001,463 (Hamburger) an allergen particulate detecting apparatus is described wherein air is blown through a passageway in which an allergen particle sensor is mounted for sensing allergen-sized particles. The output signal of the sensor is dependent on the amount of sensed particles, and an alarm is activated if the signal is above a predetermined level.
U.S. Pat. No. 5,646,597 (Hamburger, et al.) describes a system and method for detecting concentrations of particles in a given range of sizes by directing a light beam through a sample of environmental air and measuring the amount of light which is scattered by particles within the sample. A beam blocking device is provided which blocks the focused, unscattered portion of the light beam. A discriminator is also provided which allows the device to detect only those particles which are within the size range of approximately 5 to 50 microns. Pending application Ser. No. 08/771,641 providing an improvement in the discriminating apparatus of the '597 patent.
One problem with the devices described in the prior art which utilizes lasers arises when an inexpensive laser is used as the light source. In addition to the light that is focused on the beam blocking device, a certain amount of light "noise" is also produced. This noise can cause false readings if mistaken by the detector for light scattered by particles in the air sample. The present invention describes an optical configuration wherein the light noise produced by the laser is also blocked, thus preventing the device from detecting the noise as light scattered by particles in the air sample.